Exploring the Tunability and Stability of 2D Copper Phospho‐Chalcogenide CuPX (X = S, Se): A Pathway to Advanced Optoelectronic Applications

Abstract In this study, a combination of evolutionary algorithms and density functional theory (DFT) calculations is employed to discover and characterize novel 2D copper phosphochalcogenide (CuPX, X = S, Se) monolayers in six distinct structural phases: α, β, γ, δ, ε, and ζ. All predicted CuPX configurations are confirmed to be dynamically, thermodynamically, mechanically, and thermally stable. These results propose 2D‐CuPX monolayers as a promising, experimentally testable material, providing well‐defined properties and predicted behaviors to guide future synthesis and characterization. The electronic structure analysis reveals semiconducting behavior with tunable band gaps ranging from 0.03 to 1.97 eV, as calculated using the hybrid HSE06 functional. Strain engineering, through the application of ± 6% biaxial strain, enables band gap modulation and induces indirect‐to‐direct band gap transitions in the γ‐CuPS and α‐CuPSe phases. Mechanical assessments indicate Young's modulus values between 21 and 82 N·m −1 , demonstrating a balance between mechanical robustness and flexibility. Notably, the δ‐CuPSe and ζ‐CuPSe monolayers exhibit negative Poisson's ratios (NPR) of − 0.02 and − 1.03, respectively, classifying them as auxetic materials. Optical calculations based on the GW 0 + BSE method reveal strong absorption features in the visible to near‐UV range (1–5 eV), with absorption coefficients reaching up to ∼ 10.8 × 10⁵ cm −1 , attributed to interband transitions near the band edge. These properties position 2D CuPX materials as promising candidates for applications in next‐generation nanoelectronics, optoelectronic devices, strain sensors, and flexible electronics.